Systems and methods for enhanced-isolation coexisting time-division duplexed transceivers

ABSTRACT

A system for enhancing isolation in coexisting time-division duplexed (TDD) transceivers includes: a blocker canceller that transforms a transmit signal of a TDD transceiver into a blocker cancellation signal configured to remove transmit-band interference in a receive signal; a first filter that filters the blocker cancellation signal; a second filter that filters the transmit signal; and a transmit-noise canceller that transforms the filtered transmit signal into a transmit noise cancellation signal configured to remove receive-band interference in the receive signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/653,057, filed 15 Oct. 2019, which is a continuation of U.S.application Ser. No. 16/197,200, filed 20 Nov. 2018, which claims thebenefit of U.S. Provisional Application Ser. No. 62/588,864, filed on 20Nov. 2017, and of U.S. Provisional Application Ser. No. 62/714,378,filed on 3 Aug. 2018, all of which are incorporated in their entiretiesby this reference.

TECHNICAL FIELD

This invention relates generally to the wireless communications field,and more specifically to new and useful systems and methods forenhanced-isolation coexisting time-division duplexed transceivers.

BACKGROUND

Traditional wireless communication systems are half-duplex; that is,they are not capable of transmitting and receiving signalssimultaneously on a single wireless communications channel. One way thatthis issue is addressed is through the use of time division duplexing(TDD), in which transmission and reception occur on the same frequencychannel, but at different times. In many modern communication devices,two or more unsynchronized TDD operating in the same frequency band (buton different channels) exist near each other. While all radios aretransmitting or all radios are receiving, such devices work well, butwhen some radios are transmitting and some are receiving, theperformance of such devices is limited. Thus, there is a need in thewireless communications field to create new and useful systems andmethods for enhanced-isolation coexisting time-division duplexedtransceivers. This invention provides such new and useful systems andmethods.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is prior art representation of coexisting TDD transceivers;

FIG. 2A is a diagram representation of a system of an inventionembodiment;

FIG. 2B is a signal path representation of a system of an inventionembodiment;

FIG. 2C is a channel power representation of signal transformation of asystem of an invention embodiment;

FIG. 3A is a diagram representation of a system of an inventionembodiment;

FIG. 3B is a diagram representation of a system of an inventionembodiment;

FIG. 4A is a diagram representation of a system of an inventionembodiment;

FIG. 4B is a diagram representation of a system of an inventionembodiment;

FIG. 5 is a diagram representation of an analog interference cancellerof a system of an invention embodiment;

FIG. 6 is a diagram representation of a digital interference cancellerof a system of an invention embodiment; and

FIG. 7 is a diagram representation of an antenna thru-matcher of asystem of an invention embodiment.

DESCRIPTION OF THE INVENTION EMBODIMENTS

The following description of the invention embodiments of the inventionis not intended to limit the invention to these invention embodiments,but rather to enable any person skilled in the art to make and use thisinvention.

1. Coexisting Time-Division-Duplexed (TDD) Transceivers

As referenced in the background section, many modern communicationsdevices feature coexisting (i.e., having antennas in close physicalproximity to each other and configured to communicate on the samefrequency band or on frequency bands close in frequency) TDDtransceivers. For example, many wireless access points feature dual 5GHz WiFi transceivers, and most laptop computers have both a 2.4 GHzWiFi transceiver and a Bluetooth transceiver (which also operates at 2.4GHz). Still other configurations include coexisting 5 GHz WiFi, LTE,and/or MulteFire transceivers.

An example of such a communications system is as shown in FIG. 1. Notethat the transmit/receive chains of each transceiver are independent ofeach other. Further, note that when a transceiver is in receive mode,the transmit path of that receiver is not in use; when a transceiver isin transmit mode, likewise, the receive path of that receiver is not inuse.

When a transceiver is active in receive mode while another coexistingtransceiver is active in transmit mode, the receiving transceiver'sperformance is degraded. Two effects contribute to this degradation. Thefirst arises from the fact that the transmit signal of the transmittingtransceiver is much more powerful than the signal the receivingtransceiver is trying to receive. Even though the signals are ofdifferent frequencies, the signals are close enough in frequency (e.g.,in different channels of the same frequency band) that the transmitsignal can saturate the receiving transceiver (in this context, thetransmit signal is called a “blocker”). The second is because thetransmit signal is not perfectly contained within its channel, and somenoise may leak into the receive channel.

1. System for Enhanced-Isolation Coexisting TDD Transceivers

A system 100 for enhanced-isolation coexisting TDD transceivers includesat least one of the following: a tunable analog filter 110, a tunabledigital filter 111, an analog blocker canceller 120, a digital blockercanceller 121, an analog transmit-noise canceller 130, a digitaltransmit-noise canceller 131, a local oscillator (LO) exchanger 140, anantenna thru-matcher 150, and an auxiliary canceller 170. The system 100may also include any number of additional elements to enableinterference cancellation and/or filtering, including signal couplers160, amplifiers 161, frequency upconverters 162, frequencydownconverters 163, analog-to-digital converters (ADC) 164,digital-to-analog converters (DAC) 165, time delays 166, filters 167,switches 168, and any other circuit components (e.g., phase shifters,attenuators, transformers, etc.).

The system 100 functions to reduce signal degradation in coexisting TDDtransceivers by reducing interference in a receiving transceiver whilesimultaneously operating a coexisting transmitting transceiver. Thesystem 100 preferably reduces interference both by partially or fullymitigating effects of the transmit signal as a blocker signal (in thetransmit channel or otherwise) and by removing noise generated in thereceive channel by the transmit signal.

The system 100 is preferably implemented using digital and/or analogcircuitry. Digital circuitry is preferably implemented using ageneral-purpose processor, a digital signal processor, an applicationspecific integrated circuit (ASIC), a field programmable gate array(FPGA) and/or any suitable processor(s) or circuit(s). Analog circuitryis preferably implemented using analog integrated circuits (ICs) but mayadditionally or alternatively be implemented using discrete components(e.g., capacitors, resistors, transistors), wires, transmission lines,waveguides, digital components, mixed-signal components, or any othersuitable components. The system 100 preferably includes memory to storeconfiguration data, but may additionally or alternatively be configuredusing externally stored configuration data or in any suitable manner.

The system 100 may additionally or alternatively may be implemented inany manner using any optical, photonic, phonon-photonic,micro-electrical-mechanical systems (MEMS), nano-electrical-mechanicalsystems (NEMS), light, acoustic, opto-acoustic, mechanical,opto-mechanical, electrical, opto-electrical orotherwise-optically-or-acoustically-related techniques.

The system 100 may be arranged in various architectures, enablingflexibility for a number of applications. In some embodiments, thesystem 100 may be attached or coupled to existing transceivers;additionally or alternatively, the system 100 may be integrated intotransceivers. Examples of architectures of the system 100 are as shownin FIGS. 2-4B. It is understood that the system 100 may use combinationsof aspects of these architectures in various manners.

As shown in FIG. 2A, in a first implementation of an inventionembodiment, the system 100 includes two tunable analog filters 110, adigital blocker canceler 121, a digital TX noise canceller 131, an LOexchanger 140, and a plurality of couplers 160, delays 166, and switches168 (note that due to space constraints, the switches 168 are notexplicitly labeled “168”). Further note that while distinct signal pathsand switches are shown in the digital domain, this is intended toclearly show how the system 100 may route signals in multiple operatingmodes (e.g., Transceiver 1 transmitting, Transceiver 2 receiving is afirst mode; Transceiver 2 transmitting, Transceiver 1 receiving is asecond mode) rather than imply a particular digital implementation (theswitches in the digital domain may be accomplished in many ways ratherthan requiring a particular implementation).

Note that the implementation of FIG. 2A makes substantive use ofpreviously existing pathways of the coexisting transceivers; e.g., thenative local oscillators are re-used as well as parts of the un-usedreceive and transmit paths (this is clearly visible when comparing FIGS.1 and 2A). Also note that by flipping every switch of FIG. 2A, theimplementation may provide interference reduction when transceiver 1 inRX mode and transceiver 2 is in TX mode.

A signal path diagram of the implementation of FIG. 2A is as shown inFIG. 2B; this diagram can be used to explain operation of thisimplementation. The diagram begins with the transmit signal (written as“ABC”). At the output of communications device I/O 1, the label “ABC”represents three signal components of the transmit signal (A, B, andC)—while the transmit signal need not actually have three separatecomponents, this label enables one to track how various parts of thesignal are split, transformed, and recombined as they move through thesystem 100. Next, the transmit signal is split (into “AB” and “C”). Cpasses to a blocker canceller that transforms C from a transmit signalcomponent to a blocker cancellation signal C′ (i.e., a signal that canbe combined with a received signal to remove undesirable signal outsideof the receive channel). Then, C′ is filtered (to remove noise added bygeneration of the blocker cancellation signal). Meanwhile, AB passesthrough a time delay (which compensates for delay imposed by the blockercanceller) and is converted to a radio-frequency (RF) signal. AB is thensplit into A and B—A is transmitted by the transmit antenna while B isfiltered (to remove signal in the transmit band—the blocker) and thentransformed by the TX noise canceller to a TX noise cancellation signalB′ (i.e., a signal that can be combined with a receive signal to removeundesirable signal within the receive channel). A is received at thereceiver as A′ (a transformation occurs due to the wireless transmissionbetween transceiver 1 and 2) along with D (an intended receive signal).C′ is then combined with A′D to remove blocker signal. A′C′D isconverted back to digital and then combined with B′ to remove transmitnoise, resulting in the final signal A′B′C′D.

A signal power diagram of this process is as shown in FIG. 2C. As shownin FIG. 2C, the signal as received at the receiver (A′D) includesundesirable signal in both the transmit band and the receive band. WhenA′D is combined with blocker cancellation signal C′, the power ofundesirable signal in the transmit band is reduced. Then, the signalA′C′D can be converted from RF to a digital baseband signal (the processof which can further remove undesirable signal in the transmit band).Next, the signal A′C′D can be combined with the transmit noisecancellation signal B′, which reduces undesirable signal remaining inthe signal (this undesirable signal was, prior to downconversion, in thereceive band), resulting in a signal with reduced interference(A′B′C′D).

Note that while in this implementation the leftside filter 110 functionsto remove signal in the transmit band (on B) and the rightside filter110 functions to remove noise added by generation of the blockercancellation signal (on C′), these functions would be inverted if thesystem 100 were switched (e.g., to transceiver 1 in RX mode andtransceiver 2 in TX mode). This is achieved by the leftside filter 110tuned to reject T2 LO frequency, and the rightside filter 110 tuned toreject T1 LO frequency.

As shown in FIG. 3A, in a second implementation of an inventionembodiment, the system 100 includes two tunable analog filters 110, ananalog blocker canceler 120, an analog TX noise canceller 130, aplurality of couplers 160, and switches 168 (note that due to spaceconstraints, the switches 168 are not explicitly labeled “168”). Asshown, this implementation may optionally include a digital TX noisecanceller 131, an antenna thru-matcher 150, and/or an auxiliarycanceller 170.

This implementation may be useful for scenarios in which access totransceiver stages is limited (e.g., for a system 100 designed to beimplemented in the front end of a communications system/for a system 100that has limited access to analog baseband and/or digital signals); notethat in this implementation, the system 100 is coupled only to RFinput/outputs of the communication device.

In this implementation, the transmit side is sampled at RF and splitinto several signal components. The first of these (labeled A) isfiltered by a filter 110 (preferably to remove signal in the transmitband; e.g., a blocker, relaxing dynamic range requirements of thecanceller 130); next the component is downconverted to baseband using afrequency downconverter 163 operating at f2 (the current receivefrequency) and then transformed, using the TX Noise Canceller 130, intoa transmit noise cancellation signal. Optionally, a second TX noisecanceller 130/131 that samples the transmit band of the transmit signalmay be used (e.g., to remove intermodulation products present in theprimary transmit noise cancellation signal resulting from downconversionor cancellation signal generation)—note that this canceller (like allother cancellers in system 100 implementations) may be implementedeither in digital or in analog. If a canceller is implemented in thedigital domain but using analog signals, ADCs 164 and DACs 165 may beused as shown in FIG. 3A. The transmit noise cancellation signal is thenupconverted back to f2 (the current receive frequency).

The second component (labeled B) is downconverted to baseband using afrequency downconverter 163 operating at f1 (current transmitfrequency). The second component is then transformed into a blockercancellation signal by the analog blocker canceller 120, and thenfiltered by a filter 110 (to remove unwanted frequency components in thereceive band generated by blocker cancellation signal generation). (Ifthe second TX noise canceller 130/131 is present, the second componentmay also be sampled to aid in signal cancellation in the RX band asdescribed in the preceding section). Finally, the blocker cancellationsignal is converted back to RF at f1 (the current transmit frequency).

In some variations of the second implementation, the system 100 mayadditionally include an auxiliary canceller 170 operating at RF (f1 inthis case), which may be used to aid in blocker cancellation, transmitnoise cancellation, and/or any other signal cancellation desired. Forexample, a simple (i.e., having less complexity than the cancellers120/121 and/or 130/131) auxiliary canceller 170 operating at RF may behelpful in cancelling interference with short delay times betweentransmission and reception (due to a lower delay imposed by theauxiliary canceller 170).

In some variations of the second implementation, the system 100 mayadditionally include an antenna thru-matcher 150, which functions toreduce interference present at a receiver antenna by modifying couplingbetween antennas (described in more detail in later sections).

A third implementation of an invention embodiment is as shown in FIG.3B. This implementation is similar to that of FIG. 3A, except that thesystem 100 features multiple inputs and outputs, suitable for acommunication device with access to analog baseband and/or digitalpathways. In this implementation, for example, the power amplifier of atransmitter may be used to actively divide signal between a transmitantenna output and the system 100. Further, some signals (e.g., the TXnoise cancellation signal) may be combined at baseband, likewise, othersignals (e.g., output of the second TX Noise canceller 131) may becombined in the digital domain with receive signals to accomplishcancellation.

Note that the system 100 may take the form of any combination of thesetwo implementations depending on what inputs and outputs are availablefor use in a given communications system.

While the preceding examples show multi-antenna architectures, it isunderstood that the system 100 may also be implemented using duplexersand/or other circuits enabling the use of antennas by multipletransceivers. For example, an implementation of the system 100 similarto that of FIG. 3A may be implemented using a five-port duplexer(implemented with four bandpass filters no), as shown in FIG. 4A.Likewise, an implementation of the system 100 similar to that of FIG. 2Amay also be implemented using a five-port duplexer (implemented withfour bandpass filters 110), as shown in FIG. 4B.

The filters 110 and 111 function to remove or reduce the presence ofundesired frequency components within a signal. The analog filter 110 isimplemented in the analog domain, while the digital filter 111 isimplemented in the digital domain. Each filter 110/111 functions totransform signal components according to the response of the filter,which may introduce a change in signal magnitude, signal phase, and/orsignal delay.

Filters 110/111 are preferably bandpass filters, but may be any type offilter (e.g., notch filter, bandstop filter, low-pass filter, high-passfilter). Filters 110/111 are preferably analog resonant element filters,but may additionally or alternatively be any type of filter (includingdigital filters). Resonant elements of the filters 110/111 arepreferably formed by lumped elements, but may additionally oralternatively be distributed element resonators, ceramic resonators, SAWresonators, crystal resonators, cavity resonators, or any suitableresonators.

The filters 110/111 are preferably tunable such that one or more peaksof the filter 110/111 may be shifted. In one implementation of apreferred embodiment, one or more resonant elements of the filter110/111 may include a variable shunt capacitance (e.g., a varactor or adigitally tunable capacitor) that enables filter peaks to be shifted.Additionally or alternatively, filters 110/111 may be tunable by qualityfactor (i.e., Q may be modified by altering circuit control values), orfilters 110/111 may be not tunable.

Filters 110/111 may include, in addition to resonant elements, delayers,phase shifters, and/or scaling elements.

The filters 110/111 are preferably passive filters, but may additionallyor alternatively be active filters. The filters 110/111 are preferablyimplemented with analog circuit components (110), but may additionallyor alternatively be digitally implemented (111). The center frequency ofany tunable peak of a filter 110/111 is preferably controlled by atuning circuit, but may additionally or alternatively be controlled byany suitable system (including manually controlled, e.g. as in amechanically tuned capacitor).

In particular, filters 110/111 may be useful to reduce insertion losswithin a frequency range of interest. Filters 110/111 may also be usefulto reduce the power seen by noise and/or interference cancellationsystems. Note that used to enhance interference and/or noisecancellation, as opposed to independently suppressing noise (as a filtermay be used for in a system without interference and/or noisecancellation), a less-expensive, smaller, lower-quality factor (Q),and/or lower-rejection-capability filter may be used.

Filters 110/111 may additionally or alternatively be used to add timedelays to a signal (because the filters themselves may impose a timedelay upon a signal).

The blocker cancellers 120 and 121 function to remove self-interferencepresent in a receive signal (in a receive channel) due to the presenceof the transmit signal in a transmit channel (close to but typically notidentical to the receive channel). Such interference is particularly anissue where RF signals are converted to digital as part of reception(because the transmit signal, despite being in a different band, canoverwhelm the receive signal if filtering rejection is not high enoughor the receiver does not have a large enough dynamic range). The blockercancellers 120/121 function to mitigate interference present in thetransmit band of a signal using self-interference cancellationtechniques; that is, generating a self-interference cancellation signalby transforming signal samples of a first signal (typically a transmitsignal) into a representation of self-interference present in anothersignal (e.g., a receive signal, a transmit signal after amplification,etc.), due to transmission of the first signal and then subtracting thatinterference cancellation signal from the other signal.

The blocker cancellers 120/121 are preferably used to cancelinterference present in the transmit band of a receive signal; i.e., theblocker cancellers 120/121 generate an interference cancellation signalfrom samples of a transmit signal using a circuit that models therepresentation of the transmit signal, in the transmit band, as receivedby a receiver, and subtracts that cancellation signal from the receivesignal.

The blocker cancellers 120/121 may additionally be used to cancelinterference present in the transmit band (TxB) of a transmit signalsample; i.e., the blocker cancellers 120/121 generate an interferencecancellation signal from samples of a transmit signal using a circuitthat models the representation of the transmit signal, in the transmitband, as generated by a transmitter (generally, but not necessarily,before transmission at an antenna), and subtracts that cancellationsignal from the transmit signal sample. This type of interferencecancellation is generally used to ‘clean’ a transmit signal sample; thatis, to remove transmit band signal of a transmit sample, so that thesample contains primarily information in the receive band (allowing thesample to be used to perform receive-band interference cancellation).

Blocker cancellers may be implemented in analog (120), digital (121), ora combination of the two. The analog blocker canceller 120 functions toproduce an analog interference cancellation signal from an analog inputsignal. The analog blocker canceller 120 may be used to cancelinterference in any signal, using any input, but the analog blockercanceller 120 is preferably used to cancel transmit band interference inan analog receive signal. The analog blocker canceller 120 may also beused to cancel transmit band signal components in a transmit signalsample (to perform transmit signal cleaning as previously described).

Using upconverters, downconverters, ADCs, and DACs, the analog blockercanceller 120 may convert digital signals to analog input signals, andmay additionally convert interference cancellation signals from analogto digital (or to another analog signal of different frequency).

The analog blocker canceller 120 is preferably designed to operate at asingle frequency band (e.g., baseband), but may additionally oralternatively be designed to operate at multiple frequency bands. Theanalog blocker canceller 120 is preferably substantially similar to thecircuits related to analog self-interference cancellation of U.S. patentapplication Ser. No. 14/569,354 (the entirety of which is incorporatedby this reference); e.g., the RF self-interference canceller, the IFself-interference canceller, associated up/downconverters, and/or tuningcircuits, except that the analog blocker canceller 120 is notnecessarily applied solely to cancellation of interference in a receivesignal resulting from transmission of another signal (as previouslydescribed).

The analog blocker canceller 120 is preferably implemented as an analogcircuit that transforms an analog input signal into an analoginterference cancellation signal by combining a set of filtered, scaled,and/or delayed versions of the analog input signal, but may additionallyor alternatively be implemented as any suitable circuit. For instance,the analog blocker canceller 120 may perform a transformation involvingonly a single version, copy, or sampled form of the analog input signal.The transformed signal (the analog interference cancellation signal)preferably represents at least a part of an interference component inanother signal.

The analog blocker canceller 120 is preferably adaptable to changingself-interference parameters in addition to changes in the input signal;for example, transceiver temperature, ambient temperature, antennaconfiguration, humidity, and transmitter power. Adaptation of the analogblocker canceller 120 is preferably performed by a tuning circuit, butmay additionally or alternatively be performed by a control circuit orother control mechanism included in the canceller or any other suitablecontroller (e.g., by the transform adaptor of the digital blockercanceller 121).

In one implementation of a preferred embodiment, the analog blockercanceller 120 includes a set of scalers (which may perform gain,attenuation, or phase adjustment), a set of delays, a signal combiner, asignal divider, and a tuning circuit, as shown in FIG. 5. In thisimplementation the analog blocker canceller 120 may optionally includetunable filters (e.g., bandpass filters including an adjustable centerfrequency, lowpass filters including an adjustable cutoff frequency,etc.).

The tuning circuit preferably adapts the analog blocker canceller 120configuration (e.g., parameters of the filters, scalers, delayers,signal divider, and/or signal combiner, etc.) based on a feedback signalsampled from a signal after interference cancellation is performed(i.e., a residue signal). For example, the tuning circuit may set theanalog blocker canceller 120 configuration iteratively to reduceinterference present in a residue signal. The tuning circuit preferablyadapts configuration parameters using online gradient-descent methods(e.g., LMS, RLMS), but configuration parameters may additionally oralternatively be adapted using any suitable algorithm. Adaptingconfiguration parameters may additionally or alternatively includealternating between a set of configurations. Note that analog blockercancellers 120 may share tuning circuits and/or other components(although each analog blocker canceller 120 is preferably associatedwith a unique configuration or architecture). The tuning circuit may beimplemented digitally and/or as an analog circuit.

The digital blocker canceller 111 functions to produce a digitalinterference cancellation signal from a digital input signal accordingto a digital transform configuration. The digital blocker canceller 111may be used to cancel interference in any signal, using any input, butthe digital blocker canceller 111 is preferably used to cancel transmitband interference in an analog receive signal (by converting a digitalinterference cancellation signal to analog using a DAC and combining itwith the analog receive signal). The digital blocker canceller 111 mayalso be used to cancel transmit band signal components in a transmitsignal (to perform transmit signal cleaning as previously described).

Using upconverters, downconverters, ADCs, and DACs, the digital blockercanceller 111 may convert analog signals of any frequency to digitalinput signals, and may additionally convert interference cancellationsignals from digital to analog signals of any frequency.

The digital transform configuration of the digital blocker canceller 111includes settings that dictate how the digital blocker canceller 111transforms a digital transmit signal to a digital interference signal(e.g. coefficients of a generalized memory polynomial used to transforma transmit signal to an interference cancellation signal). The transformconfiguration for a digital blocker canceller 111 is preferably setadaptively by a transform adaptor, but may additionally or alternativelybe set by any component of the system 100 (e.g., a tuning circuit) orfixed in a set transform configuration.

The digital blocker canceller 111 is preferably substantially similar tothe digital self-interference canceller of U.S. Provisional ApplicationNo. 62/268,388, the entirety of which is incorporated by this reference,except in that the digital blocker canceller 111 is not necessarilyapplied solely to cancellation of interference in a receive signalresulting from transmission of another signal (as previously described).

In one implementation of a preferred embodiment, the digital blockercanceller 111 includes a component generation system, a multi-ratefilter, and a transform adaptor, as shown in FIG. 6.

The component generation system functions to generate a set of signalcomponents from the sampled input signal (or signals) that may be usedby the multi-rate filter to generate an interference cancellationsignal. The component generation system preferably generates a set ofsignal components intended to be used with a specific mathematical model(e.g., generalized memory polynomial (GMP) models, Volterra models, andWiener-Hammerstein models); additionally or alternatively, the componentgeneration system may generate a set of signal components usable withmultiple mathematical models.

In some cases, the component generator may simply pass a copy of asampled transmit signal unmodified; this may be considered functionallyequivalent to a component generator not being explicitly included forthat particular path.

The multi-rate adaptive filter functions to generate an interferencecancellation signal from the signal components produced by the componentgeneration system. In some implementations, the multi-rate adaptivefilter may additionally function to perform sampling rate conversions(similarly to an upconverter 1030 or downconverter 1040, but applied todigital signals). The multi-rate adaptive filter preferably generates aninterference cancellation signal by combining a weighted sum of signalcomponents according to mathematical models adapted to modelinterference contributions of the transmitter, receiver, channel and/orother sources. Examples of mathematical models that may be used by themulti-rate adaptive filter include generalized memory polynomial (GMP)models, Volterra models, and Wiener-Hammerstein models; the multi-rateadaptive filter may additionally or alternatively use any combination orset of models.

The transform adaptor functions to set the transform configuration ofthe multi-rate adaptive filter and/or the component generation system.The transform configuration preferably includes the type of model ormodels used by the multi-rate adaptive filter as well as configurationdetails pertaining to the models (each individual model is a model typepaired with a particular set of configuration details). For example, onetransform configuration might set the multi-rate adaptive filter to usea GMP model with a particular set of coefficients. If the model type isstatic, the transform configuration may simply include modelconfiguration details; for example, if the model is always a GMP model,the transform configuration may include only coefficients for the model,and not data designating the model type.

The transform configuration may additionally or alternatively includeother configuration details related to the signal component generationsystem and/or the multi-rate adaptive filter. For example, if the signalcomponent generation system includes multiple transform paths, thetransform adaptor may set the number of these transform paths, whichmodel order their respective component generators correspond to, thetype of filtering used, and/or any other suitable details. In general,the transform configuration may include any details relating to thecomputation or structure of the signal component generation systemand/or the multi-rate adaptive filter.

The transform adaptor preferably sets the transform configuration basedon a feedback signal sampled from a signalpost-interference-cancellation (i.e., a residue signal). For example,the transform adaptor may set the transform configuration iteratively toreduce interference present in a residue signal. The transform adaptormay adapt transform configurations and/ortransform-configuration-generating algorithms using analytical methods,online gradient-descent methods (e.g., LMS, RLMS), and/or any othersuitable methods. Adapting transform configurations preferably includeschanging transform configurations based on learning. In the case of aneural-network model, this might include altering the structure and/orweights of a neural network based on test inputs. In the case of a GMPpolynomial model, this might include optimizing GMP polynomialcoefficients according to a gradient-descent method.

Note that digital blocker cancellers 111 may share transform adaptorsand/or other components (although each digital blocker canceller 111 ispreferably associated with its own transform configuration).

The transmit-noise cancellers 130 and 131 function to removeself-interference present in a receive signal (in a receive channel) dueto the presence of the transmit signal in the receive channel (e.g., dueto noise generated in the receive channel by power amplification of thetransmit signal). The transmit-noise cancellers 130/131 function tomitigate interference present in the receive band of a signal usingself-interference cancellation techniques; that is, generating aself-interference cancellation signal by transforming signal samples ofa first signal (typically a transmit signal) into a representation ofself-interference present in another signal (e.g., a receive signal, atransmit signal after amplification, etc.), due to transmission of thefirst signal and then subtracting that interference cancellation signalfrom the other signal.

The transmit-noise cancellers 130/131 are preferably used to cancelinterference present in the receive band of a receive signal; i.e., thetransmit-noise cancellers 130/131 generate an interference cancellationsignal from samples of receive band components of a transmit signalusing a circuit that models the representation of the transmit signal,in the receive band, as received by a receiver, and subtracts thatcancellation signal from the receive signal.

The analog transmit-noise canceller 130 is preferably substantiallysimilar in structure to the analog blocker canceller 120, but mayadditionally or alternatively be any suitable analog interferencecanceller.

The digital transmit-noise canceller 131 is preferably substantiallysimilar in structure to the digital blocker canceller 121, but mayadditionally or alternatively be any suitable digital interferencecanceller.

The local oscillator exchanger 140 functions to allow the reuse of localoscillators to perform signal downconversion/upconversion tasks (thisreuse not only reduces signal complexity, but also decreases phase noisein transmitted/received signals). The local oscillator exchanger 140preferably includes switches and signal paths that allow the localoscillator from one transceiver to be coupled to the signal paths ofanother (e.g., as shown in FIG. 2A). As shown in FIG. 2A, thetransceiver 1 (T1) LO is used both to upconvert the transmitted signalto RF (@f1) and to upconvert the blocker cancellation signal (@f1 usingthe transmit chain of transceiver 2 (T2)), and the T2 LO is used both todownconvert the received signal to baseband (@f2) and to downconvert thetransmit signal samples used to generate the TX noise cancellationsignal to baseband (@f2).

The local oscillator exchanger 140 may accomplish the reuse or othersharing of local oscillators in any manner.

The antenna thru-matcher 150, as shown in FIG. 7, functions to modifycoupling between antennas to reduce the amount of interference presentat the receive antenna due to the transmit signal. The antennathru-matcher 150 preferably includes tunable analog circuit components(e.g., tunable inductors/capacitors/resistors) but may additionally oralternatively include any analog and/or digital circuit components.

Note specifically that the antenna thru-matcher 150 may be tuned not tomaximize transmission power/avoid reflection at the transmit antenna (asis typical for antenna matching networks) but may instead be tuned toreduce coupling of signal transmitted by the transmit antenna into thereceive antenna.

The antenna thru-matcher 150 is preferably tuned based on acommunication environment (e.g., specific antennas in specific locationswith specific reflection sources and signal paths) but may additionallyor alternatively not be tuned during setup/operation of the system 100or may be tuned in any manner.

Signal couplers 160 function to allow analog signals to be split and/orcombined. While not necessarily shown in the figures, signal couplersare preferably used at each junction (e.g., splitting, combining) of twoor more analog signals; alternatively, analog signals may be coupled,joined, or split in any manner. In particular, signal couplers 160 maybe used to provide samples of transmit signals, as well as to combineinterference cancellation signals with other signals (e.g., transmit orreceive signals). Alternatively, signal couplers 160 may be used for anypurpose. Signal couplers 160 may couple and/or split signals usingvarying amounts of power; for example, a signal coupler 160 intended tosample a signal may have an input port, an output port, and a sampleport, and the coupler 160 may route the majority of power from the inputport to the output port with a small amount going to the sample port(e.g., a 99.9%/0.1% power split between the output and sample port, orany other suitable split).

The signal coupler 160 is preferably a short section directionaltransmission line coupler, but may additionally or alternatively be anypower divider, power combiner, directional coupler, or other type ofsignal splitter. The signal coupler 130 is preferably a passive coupler,but may additionally or alternatively be an active coupler (forinstance, including power amplifiers). For example, the signal coupler160 may comprise a coupled transmission line coupler, a branch-linecoupler, a Lange coupler, a Wilkinson power divider, a hybrid coupler, ahybrid ring coupler, a multiple output divider, a waveguide directionalcoupler, a waveguide power coupler, a hybrid transformer coupler, across-connected transformer coupler, a resistive tee, and/or a resistivebridge hybrid coupler. The output ports of the signal coupler 160 arepreferably phase-shifted by ninety degrees, but may additionally oralternatively be in phase or phase shifted by a different amount.

Amplifiers 161 function to amplify signals of the system 100. Amplifiersmay include any analog or digital amplifiers. Some examples ofamplifiers 161 include low-noise amplifiers (LNA) typically used toamplify receive signals and power amplifiers (PA) typically used toamplify transmit signals prior to transmission.

Frequency upconverters 162 function to upconvert a carrier frequency ofan analog signal (typically from baseband to RF, but alternatively fromany frequency to any other higher frequency). Upconverters 162preferably accomplish signal upconversion using heterodyning methods,but may additionally or alternatively use any suitable upconversionmethods.

The upconverter 162 preferably includes a local oscillator (LO), amixer, and a bandpass filter. The local oscillator functions to providea frequency shift signal to the mixer; the mixer combines the frequencyshift signal and the input signal to create (usually two, butalternatively any number) frequency shifted signals, one of which is thedesired output signal, and the bandpass filter rejects signals otherthan the desired output signal. Alternatively, the upconverter 162 maynot include a filter (e.g., if filtering is provided elsewhere or is notnecessary).

The local oscillator is preferably a digital crystal variable-frequencyoscillator (VFO) but may additionally or alternatively be an analog VFOor any other suitable type of oscillator. The local oscillatorpreferably has a tunable oscillation frequency but may additionally oralternatively have a static oscillation frequency.

The mixer is preferably an active mixer, but may additionally oralternatively be a passive mixer. The mixer may comprise discretecomponents, analog integrated circuits (ICs), digital ICs, and/or anyother suitable components. The mixer preferably functions to combine twoor more electrical input signals into one or more composite outputs,where each output includes some characteristics of at least two inputsignals.

The bandpass filter (of the upconverter) is preferably a tunablebandpass filter centered around an adjustable radio frequency.Additionally, or alternatively, the bandpass filter may be a bandpassfilter centered around a set radio frequency, or any other suitable typeof filter. The bandpass filter is preferably a passive filter, but mayadditionally or alternatively be an active filter. The bandpass filteris preferably implemented with analog circuit components, but mayadditionally or alternatively be digitally implemented.

In variations in which the bandpass filter is tunable, the centerfrequency of each tunable filter is preferably controlled by a controlcircuit or tuning circuit, but may additionally or alternatively becontrolled by any suitable system (including manually controlled, e.g.as in a mechanically tuned capacitor). Each tunable bandpass filterpreferably has a set quality (Q) factor, but may additionally oralternatively have a variable Q factor. The tunable bandpass filters mayhave different Q factors; for example, some of the tunable filters maybe high-Q, some may be low-Q, and some may be no-Q (flat response).

Frequency downconverters 163 function to downconvert the carrierfrequency of an analog signal (typically to baseband, but alternativelyto any frequency lower than the carrier frequency). The downconverter163 preferably accomplishes signal downconversion using heterodyningmethods, but may additionally or alternatively use any suitabledownconversion methods.

The downconverter 163 preferably includes a local oscillator (LO), amixer, and a baseband filter. Alternatively, the downconverter 163 maynot include a filter (e.g., if filtering is provided elsewhere or is notnecessary). The local oscillator functions to provide a frequency shiftsignal to the mixer; the mixer combines the frequency shift signal andthe input signal to create (usually two) frequency shifted signals, oneof which is the desired signal, and the baseband filter rejects signalsother than the desired signal.

The local oscillator is preferably a digital crystal variable-frequencyoscillator (VFO) but may additionally or alternatively be an analog VFOor any other suitable type of oscillator. The local oscillatorpreferably has a tunable oscillation frequency but may additionally oralternatively have a static oscillation frequency.

The mixer is preferably an active mixer, but may additionally oralternatively be a passive mixer. The mixer may comprise discretecomponents, analog ICs, digital ICs, and/or any other suitablecomponents. The mixer preferably functions to combine two or moreelectrical input signals into one or more composite outputs, where eachoutput includes some characteristics of at least two input signals.

The baseband filter is preferably a lowpass filter with a tunablelow-pass frequency. Additionally or alternatively, the baseband filtermay be a lowpass filter with a set low-pass frequency, a bandpassfilter, or any other suitable type of filter. The baseband filter ispreferably a passive filter, but may additionally or alternatively be anactive filter. The baseband filter is preferably implemented with analogcircuit components, but may additionally or alternatively be digitallyimplemented.

Note that the bandpass filter of the frequency upconverter 162 and thebaseband filter of the frequency downconverter 163 are specific examplesof a filter 110 (or in).

Analog-to-digital converters (ADCs) 164 function to convert analogsignals (typically at baseband, but additionally or alternatively at anyfrequency) to digital signals. ADCs 164 may be any suitableanalog-to-digital converter; e.g., a direct-conversion ADC, a flash ADC,a successive-approximation ADC, a ramp-compare ADC, a Wilkinson ADC, anintegrating ADC, a delta-encoded ADC, a time-interleaved ADC, or anyother suitable type of ADC.

Digital-to-analog converters (DACs) 165 function to convert digitalsignals to analog signals (typically at baseband, but additionally oralternatively at any frequency). The DAC 165 may be any suitabledigital-to-analog converter; e.g., a pulse-width modulator, anoversampling DAC, a binary-weighted DAC, an R-2R ladder DAC, a cyclicDAC, a thermometer-coded DAC, or a hybrid DAC.

Time delays 166 function to delay signal components. Delays 166 may beimplemented in analog (e.g., as a time delay circuit) or in digital(e.g., as a time delay function). Delays 166 may be fixed, but mayadditionally or alternatively introduce variable delays. The delay 166is preferably implemented as an analog delay circuit (e.g., abucket-brigade device, a long transmission line, a series of RCnetworks) but may additionally or alternatively be implemented in anyother suitable manner. If the delay 166 is a variable delay, the delayintroduced may be set by a tuning circuit or other controller of thesystem 100. Although not necessarily explicitly shown in figures, delays166 may be coupled to the system 100 in a variety of ways to delay onesignal relative to another. For example, delays 166 may be used to delaya receive or transmit signal to account for time taken to generate aninterference cancellation signal (so that the two signals may becombined with the same relative timing). Delays 166 may potentially beimplemented as part of or between any two components of the system 100.

The auxiliary canceller 170 functions to aid in cancellation removal inaddition to the blocker cancellers 120/121 and transmit noise cancellers130/131. For example, a simple (e.g., single tap) auxiliary canceller170 at RF may supplement baseband cancellers 130/120 (as shown in FIG.3A). The auxiliary canceller 170 may be either analog (in which case itis preferably similar in structure to the analog blocker canceller 120)or digital (in which case it is preferably similar in structure to thedigital blocker canceller 121). The auxiliary canceller may additionallyor alternatively be any suitable interference or noise canceller.

As a person skilled in the art will recognize from the previous detaileddescription and from the figures and claims, modifications and changescan be made to the preferred embodiments of the invention withoutdeparting from the scope of this invention defined in the followingclaims.

We claim:
 1. A method for enhancing isolation in coexisting first andsecond time-division duplexed (TDD) transceivers, comprising operatingan isolation enhancement system in a first operating mode, the isolationenhancement system comprising a blocker canceller, a first TDDtransceiver local oscillator (T1 LO), a second TDD transceiver localoscillator (T2 LO), and a local oscillator (LO) exchanger, whereinoperating the isolation enhancement system in the first operating modecomprises: at the blocker canceller, sampling a transmit signal of thefirst TDD transceiver and transforming the sampled transmit signal intoa blocker cancellation signal; at a first TDD transceiver transmitchain: receiving a first local oscillator signal (LO1) from the T1 LO;and using the LO1, upconverting the transmit signal to a first frequencyband; at the second TDD transceiver, receiving a receive signal in asecond frequency band non-identical to the first frequency band; at asecond TDD transceiver transmit chain: receiving the LO1 from the T1 LOvia the LO exchanger; and using the LO1, upconverting the blockercancellation signal to an RF blocker cancellation signal in the firstfrequency band; combining the RF blocker cancellation signal with thereceive signal to generate a blocker-reduced receive signal with reducedblocker interference; and at a second TDD transceiver receive chain:receiving the second local oscillator signal (LO2) from the T2 LO; andusing the LO2, downconverting the blocker-reduced receive signal to adownconverted receive signal.
 2. The method of claim 1, furthercomprising: transitioning the isolation enhancement system from thefirst operating mode to a second operating mode; and operating theisolation enhancement system in the second operating mode, whereinoperating the isolation enhancement system in the second operating modecomprises: at the blocker canceller, sampling a second transmit signalof the second TDD transceiver and transforming the sampled secondtransmit signal into a second blocker cancellation signal; at the secondTDD transceiver transmit chain: receiving the LO2 from the T2 LO; andusing the LO2, upconverting the second transmit signal to the secondfrequency band; at the first TDD transceiver, receiving a second receivesignal in the first frequency band; at the first TDD transceivertransmit chain: receiving the Lot from the T2 LO via the LO exchanger;and using the LO2, upconverting the second blocker cancellation signalto a second RF blocker cancellation signal in the second frequency band;combining the second RF blocker cancellation signal with the secondreceive signal to generate a second blocker-reduced receive signal withreduced blocker interference; and at a first TDD transceiver receivechain: receiving the LO1 from the T1 LO; and using the LO1,downconverting the second blocker-reduced receive signal to a seconddownconverted receive signal.
 3. The method of claim 2, whereintransitioning the isolation enhancement system from the first operatingmode to the second operating mode comprises: at a first transmit switchof the LO exchanger, disconnecting a first transmit mixer of the firstTDD transceiver transmit chain from the T1 LO and connecting the firsttransmit mixer to the T2 LO; at a first receive switch of the LOexchanger, disconnecting a first receive mixer of the first TDDtransceiver receive chain from the T2 LO and connecting the firstreceive mixer to the T1 LO; at a second transmit switch of the LOexchanger, disconnecting a second transmit mixer of the second TDDtransceiver transmit chain from the T2 LO and connecting the secondtransmit mixer to the T1 LO; and at a second receive switch of the LOexchanger, disconnecting a second receive mixer of the second TDDtransceiver receive chain from the T1 LO and connecting the secondreceive mixer to the T2 LO.
 4. The method of claim 3, whereintransitioning the isolation enhancement system from the first operatingmode to the second operating mode further comprises: at a first blockercanceller switch, disconnecting the blocker canceller from a firsttransmit signal input of the first TDD transceiver; at a first DACswitch, disconnecting the first transmit signal input from the first TDDtransceiver transmit chain; at a second blocker canceller switch,connecting the blocker canceller to a second transmit signal input ofthe second TDD transceiver; and at a second DAC switch, connecting thesecond transmit signal input to the second TDD transceiver transmitchain.
 5. The method of claim 2, wherein operating the isolationenhancement system in the first operating mode further comprises:splitting the upconverted transmit signal into a first transmit portionand a first cancellation portion; downconverting the first cancellationportion into a first downconverted transmit signal; at a transmit-noisecanceller, transforming the first downconverted transmit signal into afirst transmit-noise cancellation signal configured to remove secondfrequency band interference in the receive signal; and combining thefirst transmit-noise cancellation signal with the receive signal,thereby reducing interference in the receive signal; wherein operatingthe isolation enhancement system in the second operating mode furthercomprises: splitting the upconverted second transmit signal into asecond transmit portion and a second cancellation portion;downconverting the second cancellation portion into a seconddownconverted transmit signal; at the transmit-noise canceller,transforming the second downconverted transmit signal into a secondtransmit-noise cancellation signal configured to remove first frequencyband interference in the second receive signal; and combining the secondtransmit-noise cancellation signal with the second receive signal,thereby reducing interference in the second receive signal.
 6. Themethod of claim 5, wherein: operating the isolation enhancement systemin the first operating mode further comprises, before downconverting thefirst cancellation portion, at a first bandpass filter, filtering thefirst cancellation portion to remove power in the first frequency band;and operating the isolation enhancement system in the second operatingmode further comprises, before downconverting the second cancellationportion, at a second bandpass filter, filtering the second cancellationportion to remove power in the second frequency band.
 7. The method ofclaim 6, wherein operating the isolation enhancement system in the firstoperating mode further comprises: coupling the first transmit portion toan antenna via a third bandpass filter, wherein the third bandpassfilter is configured to pass the first frequency band; at the antenna,transmitting the first transmit portion and receiving the receivesignal; and coupling the receive signal from the antenna to the secondTDD transceiver receive chain via a fourth bandpass filter, wherein thefourth bandpass filter is configured to pass the second frequency band.8. The method of claim 7, wherein operating the isolation enhancementsystem in the second operating mode further comprises: coupling thesecond transmit portion to the antenna via the fourth bandpass filter,wherein the fourth bandpass filter is configured to pass the secondfrequency band; at the antenna, transmitting the second transmit portionand receiving the second receive signal; and coupling the second receivesignal from the antenna to the first TDD transceiver receive chain viathe third bandpass filter, wherein the third bandpass filter isconfigured to pass the first frequency band.
 9. The method of claim 6,wherein: operating the isolation enhancement system in the firstoperating mode further comprises, before combining the RF blockercancellation signal with the receive signal, at the second bandpassfilter, filtering the RF blocker cancellation signal to remove noise inthe second frequency band; and operating the isolation enhancementsystem in the second operating mode further comprises, before combiningthe second RF blocker cancellation signal with the second receivesignal, at the first bandpass filter, filtering the second RF blockercancellation signal to remove noise in the first frequency band.
 10. Themethod of claim 1, wherein operating the isolation enhancement system inthe first operating mode further comprises: splitting the upconvertedtransmit signal into a first transmit portion and a first cancellationportion; at a first bandpass filter, filtering the first cancellationportion to remove power in the first frequency band; after filtering thefirst cancellation portion, downconverting the first cancellationportion into a first downconverted transmit signal; at a transmit-noisecanceller, transforming the first downconverted transmit signal into afirst transmit-noise cancellation signal configured to remove secondfrequency band interference in the receive signal; and combining thefirst transmit-noise cancellation signal with the receive signal,thereby reducing interference in the receive signal.
 11. The method ofclaim 10, wherein operating the isolation enhancement system in thefirst operating mode further comprises: coupling the first transmitportion to an antenna via a second bandpass filter, wherein the secondbandpass filter is configured to pass the first frequency band; at theantenna, transmitting the first transmit portion and receiving thereceive signal; coupling the receive signal from the antenna to thesecond TDD transceiver receive chain via a third bandpass filter,wherein the third bandpass filter is configured to pass the secondfrequency band.
 12. A system for enhancing isolation in coexisting firstand second time-division duplexed (TDD) transceivers, the systemoperable to switch between a first operating mode and a second operatingmode, the system comprising: a first signal path; a first cancellationpath; a second signal path; a second cancellation path; a first couplerconnected to the first signal path and the first cancellation path; asecond coupler connected to the second signal path and the secondcancellation path; and a transmit-noise canceller; wherein, in the firstoperating mode: the first coupler splits a first transmit signal of thefirst TDD transceiver into a first transmit portion, coupled into thefirst signal path, and a first cancellation portion, coupled into thefirst cancellation path; the transmit-noise canceller receives the firstcancellation portion via the first cancellation path and transforms thefirst cancellation portion into a first transmit-noise cancellationsignal configured to remove first receive-band interference in a firstreceive signal of the second TDD transceiver; the first transmit signalis transmitted in a first frequency band; the first receive-bandinterference is in a second frequency band non-identical to the firstfrequency band; the first receive signal is received in the secondfrequency band; and the system combines a first set of cancellationsignals, comprising the first transmit-noise cancellation signal, withthe first receive signal of the second TDD transceiver, resulting ingeneration of a first reduced-interference receive signal; wherein, inthe second operating mode: the second coupler splits a second transmitsignal of the second TDD transceiver into a second transmit portion,coupled into the second signal path, and a second cancellation portion,coupled into the second cancellation path; the transmit-noise cancellerreceives the second cancellation portion via the second cancellationpath and transforms the second cancellation portion into a secondtransmit-noise cancellation signal configured to remove secondreceive-band interference in a second receive signal of the first TDDtransceiver; the second transmit signal is transmitted in the secondfrequency band; the second receive-band interference is in the firstfrequency band; the second receive signal is received in the firstfrequency band; and the system combines a second set of cancellationsignals, comprising the second transmit-noise cancellation signal, withthe second receive signal of the first TDD transceiver, resulting ingeneration of a second reduced-interference receive signal.
 13. Thesystem of claim 12, further comprising: a first bandpass filterconnected along the first cancellation path, wherein, in the firstoperating mode, the first bandpass filter filters the first cancellationportion to remove power in the first frequency band; and a secondbandpass filter connected along the second cancellation path, wherein,in the second operating mode, the second bandpass filter filters thesecond cancellation portion to remove power in the second frequencyband.
 14. The system of claim 13, wherein the first signal path and thesecond signal path are coupled to an antenna, the system furthercomprising: a third bandpass filter connected along the first signalpath, the third bandpass filter configured to remove power in the secondfrequency band; and a fourth bandpass filter connected along the secondsignal path, the fourth bandpass filter configured to remove power inthe first frequency band.
 15. The system of claim 14, wherein, in thefirst operating mode: the third bandpass filter filters the firsttransmit portion; after the third bandpass filter filters the firsttransmit portion, the first transmit portion is coupled into theantenna; the first receive signal is received from the antenna; and thefourth bandpass filter filters the first receive signal; wherein, in thesecond operating mode: the fourth bandpass filter filters the secondtransmit portion; after the fourth bandpass filter filters the secondtransmit portion, the second transmit portion is coupled into theantenna; the second receive signal is received from the antenna; and thethird bandpass filter filters the second receive signal.
 16. The systemof claim 12, further comprising a blocker canceller, wherein: in thefirst operating mode, the blocker canceller samples the first transmitsignal and transforms the sampled first transmit signal into a firstblocker cancellation signal, wherein the first set of cancellationsignals further comprises the first blocker cancellation signal; and inthe second operating mode, the blocker canceller samples the secondtransmit signal and transforms the sampled second transmit signal into asecond blocker cancellation signal, wherein the second set ofcancellation signals further comprises the second blocker cancellationsignal.
 17. The system of claim 13, further comprising a localoscillator (LO) exchanger, a first TDD transceiver local oscillator (T1LO), a second TDD transceiver local oscillator (T2 LO), a first mixer, asecond mixer, a third mixer, and a fourth mixer, wherein, in the firstoperating mode: the first mixer receives a first local oscillator signal(LO1) from the T1 LO and, using the LO1, upconverts the first transmitsignal to the first frequency band; the third mixer receives a secondlocal oscillator signal (LO2) from the T2 LO via the LO exchanger and,using the LO2, downconverts the first cancellation signal, wherein thetransmit-noise canceller transforms the first cancellation portion intothe first transmit-noise cancellation signal after the third mixerdownconverts the first cancellation signal; and the fourth mixerreceives the LO2 from the T2 LO and, using the LO2, downconverts thefirst receive signal, wherein the system combines the firsttransmit-noise cancellation signal with the first receive signal afterthe fourth mixer downconverts the first receive signal; wherein, in thesecond operating mode: the second mixer receives the LO2 from the T2 LOand, using the LO2, upconverts the second transmit signal to the secondfrequency band; the fourth mixer receives the LO1 from the T1 LO via theLO exchanger and, using the LO1, downconverts the second cancellationsignal, wherein the transmit-noise canceller transforms the secondcancellation portion into the second transmit-noise cancellation signalafter the fourth mixer downconverts the second cancellation signal; andthe third mixer receives the LO1 from the T1 LO and, using the LO1,downconverts the second receive signal, wherein the system combines thesecond transmit-noise cancellation signal with the second receive signalafter the third mixer downconverts the second receive signal.
 18. Thesystem of claim 17, further comprising a blocker canceller, wherein, inthe first operating mode: the blocker canceller samples the firsttransmit signal and transforms the sampled first transmit signal into afirst blocker cancellation signal, wherein the first set of cancellationsignals further comprises the first blocker cancellation signal; and thesecond mixer receives the LO1 from the T1 LO via the LO exchanger and,using the LO1, upconverts the first blocker cancellation signal to thefirst frequency band, wherein the system combines the first blockercancellation signal with the first receive signal after the second mixerupconverts the first blocker cancellation signal and before the fourthmixer downconverts the first receive signal; wherein, in the secondoperating mode: the blocker canceller samples the second transmit signaland transforms the sampled second transmit signal into a second blockercancellation signal, wherein the second set of cancellation signalsfurther comprises the second blocker cancellation signal; and the firstmixer receives the LO2 from the T2 LO via the LO exchanger and, usingthe LO2, upconverts the second blocker cancellation signal to the secondfrequency band, wherein the system combines the second blockercancellation signal with the second receive signal after the first mixerupconverts the second blocker cancellation signal and before the thirdmixer downconverts the third receive signal.
 19. The system of claim 18,further comprising: a first bandpass filter, wherein, in the firstoperating mode, the first bandpass filter filters the first blockercancellation signal, thereby reducing signal power in the firstfrequency band; and a second bandpass filter, wherein, in the secondoperating mode, the second bandpass filter filters the second blockercancellation signal, thereby reducing signal power in the secondfrequency band.
 20. The system of claim 19, wherein: the first andsecond bandpass filters are tunable; in the first operating mode, thesecond bandpass filter is tuned to reduce signal power in the firstfrequency band, wherein the second bandpass filter receives the firstcancellation portion via the first cancellation path, filters the firstcancellation portion, and couples the first cancellation portion to thetransmit-noise canceller; and in the second operating mode, the firstbandpass filter is tuned to reduce signal power in the second frequencyband, wherein the first bandpass filter receives the second cancellationportion via the second cancellation path, filters the secondcancellation portion, and couples the second cancellation portion to thetransmit-noise canceller.